1. Field of the Invention
The present invention relates to a circuit device which improves the heat dissipation of a resin package.
2. Description of the Related Art
As one example of a conventional method of manufacturing a circuit device, the following manufacturing method has been known. As shown in FIG. 6A, a circuit board 51 made of a metal substrate such as an A1 substrate is prepared, and an insulative resin layer 52 and a conductive pattern 53 are formed on an upper surface of the circuit board 51. Further, circuit elements 54 and leads 55 are electrically connected to the top of the conductive pattern 53 to form a hybrid integrated circuit on the circuit board 51. Then, the circuit board 51 is placed in a cavity 57 of a resin encapsulation mold 56, and the leads 55 are clamped between an upper mold half 58 and a lower mold half 59. Thus, the circuit board 51 is fixed in the cavity 57.
As shown in FIG. 6B, resin is injected into the cavity 57 through a gate portion 60 of the resin encapsulation mold 56. At this time, as indicated by an arrow 61, the injected resin collides against a side surface of the circuit board 51 first. The resin flows to the upper and lower surface sides of the circuit board 51 as indicated by arrows 61A and 61B. Further, a curved surface 62 is disposed at an edge portion of the lower surface of the circuit board 51, and therefore the resin is allowed to efficiently flow to the lower surface side of the circuit board 51. Although the thickness of a resin encapsulant under the lower surface of the circuit board 51 is, for example, approximately 0.5 mm, the aforementioned resin injection method enables the narrow gap to be filled with the resin. This technology is described for instance in Japanese Patent Application Publication No. 2003-17515 (pages 6 to 9, and FIGS. 8 and 9).
Moreover, as one example of a conventional circuit device, the following structure has been known. As shown in FIG. 7, in a circuit device 71, a hybrid integrated circuit including a conductive pattern 73 and circuit elements 74 is constructed on an upper surface of a circuit board 72, and the upper, side, and lower surfaces of the circuit board 72 are integrally covered with a resin encapsulant 75. Further, the resin encapsulant 75 includes a first resin encapsulant 75A formed by transfer molding and a second resin encapsulant 75B formed by melting a solid resin sheet. It should be noted that as shown in the drawing, from side surfaces of the resin encapsulant 75, leads 76 electrically connected to the conductive pattern 73 on the upper surface of the circuit board 72 are led out of the resin encapsulant 75. This technology is described for instance in Japanese Patent Application Publication No. 2010-67852 (pages 4 to 10, and FIGS. 1 to 4).
First, in the manufacturing method described with reference to FIGS. 6A and 6B, the resin injected through the gate portion 60 of the resin encapsulation mold 56 collides against a side surface of the circuit board 51, and the utilization of the curved surface 62 formed in the circuit board 51 makes it easy to fill a narrow region under the lower surface of the circuit board 51 with the resin. Further, to prevent the formation of an incompletely filled region in the narrow region under the lower surface of the circuit board 51, a width enough to allow the flow of the resin is needed. Thus, there is the problem that it is difficult to realize a reduction in the thickness of the resin encapsulant under the lower surface of the circuit board 51, and to improve the heat dissipation from the resin encapsulant.
In particular, conceivable ways to solve this problem of heat dissipation include increasing the filler content in resin for encapsulation and increasing the particle size of the filler. However, increasing the filler content or increasing the particle size thereof causes another problem that the flowability of the resin deteriorates to make an incompletely filled region more likely to be formed under the lower surface of the circuit board 51. Furthermore, with regard to the material and shape of the filler used, manufacturing methods in which all the surfaces of the circuit board 51 are integrally encapsulated in a single type of resin also have problems such as damage to circuit elements and breakage in fine metal wires, thus having the problem that the material and shape thereof are limited.
Next, in the circuit device 71 described with reference to FIG. 7, though an incompletely filled region is prevented from being formed under the lower surface of the circuit board 72, and a reduction in the thickness of the resin encapsulant is realized, no disclosure is made with regard to a structure for further improving heat dissipation.